_Development.—_The carbon prints are developed either on a sheet of paper upon which it should remain (single or simple transfer), or on a provisory support to be afterwards transferred on paper or any other material (double transfer).
_Simple Transfer.—_This process is quite simple: The impressed tissue and a sheet of paper coated with alumed (insoluble) gelatine are immersed face to face in cold water, and when the tissue is softened both are removed, one superposed on the other, and the whole, being placed on a glass plate and covered with a thin oil cloth, is firmly pressed into contact with the squeegee. The rationale of applying under water the tissue on the gelatinized paper is to avoid the interposition of air bubbles.
To operate by simple transfer the tissue should be impressed under a reversed negative. The reason is obvious.
_Double Transfer.—_By this method the carbon prints are generally developed on porcelain or opal plates, which more easily than glass plates permit one to follow the progress of the development and to retouch the imperfections before transferring the picture on paper.
In order that the image does not adhere on the provisory support a little of the following mixture is spread over the plate, which is then pretty strongly heated, and, when it has cooled down, polished lightly with a piece of white flannel to obtain a very thin and even layer free from striæ. If the plate has not been used before for the purpose in question, it should be waxed a second time in the same manner:
Yellow wax 4 parts Rosin 1 part Turpentine or benzine 250 parts
The plates can be developed on the plates so waxed, but for “full gloss,” that is, for enameled pictures, a film of collodion is applied on the plates, which then, instead of being waxed, should to be simply flowed with a solution of India rubber 1 to 100 of benzole:
Ether 250 parts Alcohol 250 parts Castor oil 1 part Pyroxyline 5 to 6 parts
When the plate is coated and the collodion film set, it is immersed in water until greasiness has disappeared and wanted for use. Then the tissue, previously soaked in water, is applied upon it (taking care to avoid air bubbles) and squeezed, lightly at first, with some force afterwards, to insure a perfect contact.